Despite the gradual arrival of fall, mosquitos are still active in our state. Paulo Verardi, professor of virology and vaccinology and head of the Department of Pathobiology and Veterinary Science, shares information that can keep Connecticut residents safe from mosquito-borne diseases.
What types of mosquito-borne diseases are we seeing in Connecticut?
Mosquito-borne diseases are spread by the bite of infected mosquitoes. In Connecticut, one would immediately think of West Nile virus, by far the most common mosquito-borne virus in the region. However, we have 
additional viruses transmitted by mosquitoes, such as Eastern Equine Encephalitis (EEE) virus, Jamestown Canyon virus, and Cache Valley virus, that luckily are less common. Sometimes Connecticut has imported cases of additional mosquito-borne diseases, such as dengue fever and Zika virus disease. These are acquired when people travel to areas where the virus is circulating, get bitten by an infected mosquito, and then travel back to Connecticut. If you are traveling outside the country in areas like the Caribbean and Central or South America, you should also be aware of chikungunya virus, yellow fever virus, and Oropouche virus, to name a few.
Why are these diseases appearing more frequently in the state?
Cases are linked to the proliferation of mosquitoes, which is driven by several factors including precipitation and temperature patterns, as well as alterations in these patterns. Climatic changes seem to also be impacting the distribution of these diseases, especially because warmer temperatures can promote a wider geographical range of disease-transmitting mosquitoes.
West Nile virus has been in Connecticut since 1999, when it was introduced in New York City, so it is relatively new. On the other hand, evidence of EEE in Massachusetts dates back almost 200 years, and thus it is considered a local disease. West Nile cases in people are not uncommon during every mosquito season, but EEE seems to be impactful only every few years, such as in 2019 when a larger outbreak last occurred.
West Nile and EEE viruses are actually maintained in nature in reservoir hosts, typically birds, and therefore these are considered zoonotic diseases. This means that the interplay amongst people, animals, plants, and the environment is a major factor determining the prevalence and transmission of these diseases, in what we call the One Health concept.
What times of year do we need to be concerned about mosquito-borne diseases?
We ought to be concerned any time of the year when mosquitoes are up and about. Generally, we think of the hot summer months, but transmission can start in the spring and last well into the fall season. A good example is EEE, as cases typically peak in late summer, but transmission can occur as late as October.
What are the symptoms of these diseases?
Diseases like West Nile and EEE are caused by viruses, so flu-like symptoms are typical: fever, headache, fatigue, and in some instances rashes. Most people may not even feel sick at all, while a few others may end up developing inflammation of the brain (encephalitis) or of the membranes around the brain and the spinal cord (meningitis), leading to severe disease symptoms.
What should someone do if they are sick?
First, never assume that you may just have a cold, and pay attention to the severity of your symptoms. Consult a health care provider if symptoms do not improve, particularly if you have high fever and headache. Go immediately to an emergency room if symptoms become severe and you suspect any neurological involvement. The key is to be vigilant and proactive.
It is noteworthy that horses with EEE are severely affected with up to 95% mortality (about half that rate for West Nile fever), and routine vaccination of horses for both diseases is recommended.
How dangerous/deadly are these diseases?
Fortunately, for most of us infections are self-contained. Our immune system can keep the invading viruses in check, and all you may experience are mild flu-like symptoms, if any. But symptoms can be more severe and can worsen very quickly. Pay attention to any rashes or severe symptoms, such as high fever, intense headache, stiffness of the neck, and other neurological problems. Encephalitis and meningitis are dangerous and life-threating complications, so a visit to the emergency room is necessary at the onset of neurological signs.
What actions are state and local governments taking to help?
Connecticut’s Department of Public Health (DPH) and Department of Agriculture (DoAg) are monitoring the situation in Connecticut and surrounding states closely. The Connecticut Agricultural Experiment Station (CAES) is doing surveillance of mosquitoes, and the Connecticut Veterinary Medical Diagnostic Laboratory (CVMDL) at UConn is monitoring wild and domestic animals (mammals and birds). In some cases, agencies may decide to curtail outdoor activities in certain areas at dusk, as Connecticut did in 2019 when we had high activity of EEE in Eastern Connecticut CT and neighboring states, and mosquito spraying may be recommended in limited areas by the Connecticut’s Department of Energy and Environmental Protection (DEEP).
How can Connecticut residents protect themselves and help stop the spread of these diseases?
- Avoid outdoor activities during dusk and dawn, when mosquitoes are most active
- Use approved insect repellents
- Wear long-sleeved shirts and pants when outside
- Keep mosquitoes out of your house with the appropriate use of window and door screens.
One can also treat clothing and gear with permethrin, which will help repel both mosquitoes and ticks. Vaccines against some mosquito-borne illnesses such as dengue, yellow fever, chikungunya, and Japanese encephalitis are available for people traveling to high-risk areas. Visit the Center for Disease Control and Prevention (CDC) Traveler’s Health site for further information.
This work relates to CAHNR’s Strategic Vision area focused on Enhancing Health and Well-Being Locally, Nationally, and Globally.
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